The present invention relates to a connector system for connection of leadless large scale integrated circuit (LSI) devices to a printed circuit board or to other termination means and comprises a leadless ceramic carrier, a leaded socket and a cover member. Contact is made between the pads on the leadless LSI carrier and a printed circuit board through contact elements carried by the leaded socket.
Semiconductors and printed circuitry have greatly affected the electronic industry. The increase in circuit density in electronic devices achieved thereby has stepped up the demand for denser termination and contact patterns. Recent advances in LSI technology has made it possible to produce electronic circuitry which is so dense that a single chip may contain from 20,000 to 50,000 transistors.
For a number of years, the dual in line (DIP) package configuration has been the package of choice in the electronic industry. Designs with up to 64 leads have been used, but the most popular sizes have 40 pins or less. The increased capability of LSI technology and the accompanying increased system complexities have increased the demand for packages with greater than 40-pin counts. The DIP comprises a main body which houses the integrated circuit and has two parallel rows of leads or "legs" coming off both sides of the body.
Mounting of the DIP on a printed circuit board has traditionally been accomplished by soldering the legs directly to the board or by being plugged into a socket which has been soldered into place on the board. While soldering provides very reliable gas tight electrical connections, it also makes assembly and removal of the package difficult due to the necessity of applying heat. The heat necessary to form the solder connection is quickly conducted through the leads into the integrated circuit package which may cause overheating thereof. Overheating can cause cracks in the glass seal and can damage the integrated circuit. Heat also can warp and/or cause delamination of the printed circuit board. The application of heat is relatively easy to control during initial assembly of the circuit board under factory conditions. However, many costly elements and wiring board assemblies have been destroyed by the application of excessive heat at installation sites.
Another package, the leadless carrier, offered a number of advantages over the traditional DIP. First, there are no legs which means lower initial cost and higher manufacturing yields. Second, leadless carriers are significantly smaller than equivalent DIPs which thus permits higher packaging densities and shorter lead lengths.
Just as with DIPs, unsoldering a leadless carrier at an installation site is very undesirable. Due to the problems of replacement inherent with solder connections, many types of demountable connectors have been developed which do not require the use of heat in the formation of the electrical connections. These connectors employ what may be called pressure contacts for the formation of the electrical connections.
In general, connectors which are soldered in place require solder leads or legs for the connector and require minimum contact centers of about 0.10 inch to avoid solder bridging across adjacent pads on the circuit board. Connection pads on the carrier may be formed either along the edge, top or bottom. In all cases, however, the pluggable connection is made by pressing individual metal contacts against pads on the carrier. The need for individual metal contacts has meant that the connector must inevitably be large enough to accommodate and separate each of the individual contacts. The contacts themselves must be large enough to supply adequate spring force to insure a good electrical connection. In addition to these constraints, the precision stamping and assembly requirements have proved to be quite expensive.
Other problems encountered with the DIPs described hereinabove have included high thermal resistance, high pin-to-pin capacitance and high lead resistance due to the long lead lengths especially in the high pin count DIPs.